graceful failure if user's Java is too old

[garfieldnate]

Right now if the user tries to run the debugger, for example, with Java 8, no errors are printed out, but a dialog box pops up saying "Java Virtual Machine Launcher: A Java Exception has occurred". We should detect if the Java version is lower than 11 and tell the user that they need a newer Java.

Obviously it would be even better to just include a JVM with jlink or something, but that's a larger task.